The invention relates to the redundancy of network elements and to load balancing in a telecommunications system, and especially to using parallel gateway nodes, such as GGSNs (Gateway GPRS support node) in a packet-switched mobile system. To provide a concrete example, the invention will be described in the context of a packet-switched mobile communication system.
The continuous development of applications transmitted in mobile systems sets ever increasing demands on mobile networks. An efficient use of the radio network determining the capacity of the system is important to enable extensive traffic. Packet-switched connections are more efficient than circuit-switched connections in many applications. They are especially well suited for burst data transmission, such as for the use of the Internet. A high bit rate is then required to load a new page, but, on the other hand, data traffic is almost non-existent when the page is viewed. In circuit-switched connections, the capacity of the connection is, however, all the time reserved for a certain user, whereby resources are wasted and the user must also pay for this. In a packet-switched system, resource allocation is based on the amount of transmitted data and not the duration of the connection.
GPRS (General packet radio service) is a technique enabling packet-switched data transmission that will be utilized in the third-generation mobile network UMTS (Universal mobile telecommunications system), for instance. GPRS requires the introduction of new network elements, such as GGSN, in the mobile system. GGSN is the network element of the GPRS and UMTS mobile networks and controls the routing of data packets in the GPRS network and takes care of connecting the GPRS network to other networks, such as the Internet and other GPRS networks.
In the GPRS system, the logical connection between a mobile station and GGSN supporting the mobile station is called a PDP (Packet data protocol) context. A redundant GGSN node comprises several GTP-U (GPRS tunnelling protocol-User plane) and GTP-C (GPRS tunnelling protocol-Control plane) processing units that apply packet transmission based on PDP contexts. Redundancy is used in the GTP-U and GTP-C processing units to continue transmitting packets even in error situations. The redundancy is based on having a second processing unit take over, if the primary unit cannot continue transmitting packets. The redundancy of network nodes, such as GGSN, is typically implemented using backup units with a redundancy ratio of 1:1, whereby there is one backup unit for each active unit. The problem with 1:1 redundancy is that it makes the structure of the network node heavy and expensive, if every processing unit is to be backed up.